Method of shutting down the gas generator



Dec. 31,1957 DU B018 EASTMAN EI'AL ,8 8,

METHOD 0% SHUTTING DOWN THE GAS GENERATOR Filed Aug. '7; 1956 l llMETHOD OF SHUTTING DOWN THE GAS GENERATOR Du Bois Eastman and William L.Slater, Jr., Whittier, Calif., assignors to The Texas Company, New York,N. Y., a corporation of Delaware Application August 7, 1956, Serial No.602,652

6 Claims. (Cl. 48-496) This invention relates to the production of hightemperature gases at elevated pressure and more particularly to quenchcooling or scrubbing high temperature gases at elevated pressure. In oneof its more specific aspects the invention relates to the production ofcarbon monoxide and hydrogen, or synthesis gas, wherein a carbonaceousfuel is subjected to reaction with an oxidizing gas comprising freeoxygen at an elevated temperature and at superatrnospheric pressure andwherein the hot resulting products of reaction are cooled by directcontact with liquid water in an amount in excess of the amount which maybe vaporized in cooling the gas stream.

carbonaceous fuels, including gaseous and liquid hydrocarbons and solidfuels, such as coal, coke and lignite, may be converted to carbonmonoxide and hydrogen by reaction with an oxidizing gas comprising freeoxygen. Air, oxygen-enriched air, or substantially pure oxygen may beemployed as the source of free oxygen. Generally, substantially pureoxygen is preferred. With the heavier carbonaceous fuels, i. e. liquidand solid fuels, it is generally desirable to react the fuel with amixture of free oxygen and steam, whereas in the case of gaseous fuels,the presence of steam, although optional, is usually not desirable.Recently a process has been developed for non-catalytic reaction ofcarbonaceous fuels with free oxygen in a flow-type reaction zone. (See,for example, 2,701,756, Eastman et al., and 2,655,443, Moore.) Thegeneration of synthesis gas may be carried out at elevated pressureswhich may range as high as 800 to 1000 p. s. i. g., preferably 100 to500 p. s. i. g., and at temperatures in the range of 2000 to 3500 F.Partial oxidation of the carbonaceous fuel under these conditions mayeffect substantially complete conversion of the fuel to carbon monoxideand hydrogen. Small amounts of carbon dioxide, light hydrocarbons andfree carbon are generally contained in the raw product gas.

In the generation of synthesis gas, i. 6. carbon monoxide and hydrogen,by partial oxidation, it is desirable to quench the hot gas leaving thereaction chamber from the reaction temperature which is above 2000 F. toa temperature below about 600 F. in a very short period of time.Quenching the hot gases freezes the composition of the product gas andsubstantially prevents degradation reactions which take place on slowcooling. The degradation reactions generally result in the formation offree carbon and hydrocarbons. It is preferable to quench the product gasfrom the gas generator by direct contact at substantially generatorpressure with liquid water maintained in a suitable reservoir into whichthe hot gases are conducted and discharged at a point below the surfaceof the liquid.

This method of quenching, while entirely satisfactory, presents aproblem when the generator is shut down to prevent the entry of liquidwater from the quench vessel into the reaction chamber. The danger ofpermitting liquid water to come into contact with the refract ory icelining of the synthesis gas generator, which is generally at atemperature considerably in excess of 2000 F. when the generator is shutdown, is obvious. The temperature maintained in the quench vessel is notabove about 550 F., and generally, less than 500 F. In any case, thequench water temperature is not above the temperature corresponding tothe boiling point of water at the pressure existing in the quench zone,which is substantially equal to the pressure in the gas generator.

If the flow of reactants to the gas generation zone is interrupted whilecontinuing withdrawal of reaction products therefrom so that thepressure in the gas generation zone and associated water quench coolingzone is permitted to decline, the point is soon reached at which thepressure in the gas generation zone and water quench cooling zone isbelow the vapor pressure of the water in the cooling zone. When thepressure falls below the boiling point of water in the cooling zone,steam flashes from the water and may be forced up into the hotgenerator. This is a very dangerous condition which may very easily leadto destruction of the hot refractory insulation within the gasgenerator. The condition may be avoided by depressuring the generatorand quench system while continuing to feed reactants so that the steamflashed off from the water in the quench zone is carried away withproduct gases. This method has two disadvantages. First, the product gasmust generally be vented, since under normal operations the gas isdelivered at a pressure of several hundred pounds per square inch andcompressors and other equipment are designed to handle gas only atelevated pressure. Second, it may be imperative that the gas generatorbe shut down quickly due to failure of gas or oxygen supply or dangerouscon- 'dition of equipment.

We have found that the gas generator may be shut down immediately whileavoiding the danger of introducing water or steam into the hotgenerator. This is accomplished by discontinuing the introduction ofreactants to the gas generation zone and simultaneously discontinuingthe withdrawal of reaction products therefrom and from the associatedpressurized quench zone. The generator and quench zone are thus bottledup so that there is no substantial reduction in pressure in either thegas generator or the quench zone. At the same time cooling water iscontinuously supplied to and withdrawn from the cooling zone, or quenchzone, at a temperature below the temperature corresponding to theboiling point of the water at the existing pressure. (Often hot water issupplied to the gas cooling and quench zone during normal operation.)The pressure is then gradually reduced in the reaction zone and coolingzone by withdrawal of gas therefrom at a rate such that the pressure inthe reaction zone is maintained at all times in excess of the vaporpressure of the water in the cooling zone. Generally, in shutting downthe gas generators it is desir able to bring the pressure of thegenerator and associated quench system down to atmospheric pressure.This is accomplished by introduction of cool water, i. e. water at atemperature below 212 F., into the cooling zone, and withdrawal of watertherefrom, until the temperature of the water in the cooling zone isreduced below the atmospheric boiling point or below about 212 F.Pressure reduction in the gas generator and quench system isaccomplished by venting gas therefrom, preferably from the water quenchvessel, until the pressure is reduced to the desired pressure, generallyatmospheric pressure.

The invention will be more readily understood by reference to theaccompanying drawing.

The figure is an elevational view in cross section of an illustrativegas generator and associated cooling or quench vessel. Although theapparatus illustrated is particularly Patented Dec. 31, 1957 adapted forthe generation of synthesis gas from liquid hydrocarbons, the principlesof operation described in connection therewith apply generally tosimilar operations in which a high temperature gas is generated atelevated pressure and is brought into intimate contact with -a volatilecooling liquid, e. g. water or oil. Apparatus for the generation andquench cooling of gases comprising carbon monoxide fromtgaseous or solidfuels are generally similar to the illustrated apparatus. In case ofsolid fuel having a fusible ash, provision may be made for separatelycollecting and cooling the slag, not, per se, a part of the presentinvention.

With reference to the figure, the gas generator 1 comprises .a pressurevessel 2 provided with a suitable refractory and heat insulating lining3 enclosing a compact, unpacked reaction chamber 10. A dispersion of oilin steam is passed through .line v4, controlled by valve 5 into asuitable mixer-burner 6. Oxygen from line 3, controlled by valve 9, isseparately admitted into burner 6. Steam, oil and oxygen are introducedthrough burner 6 into the reaction zone into intimate admixture with oneanother. Partial combustion takes place within the reaction zone at hightemperature and elevated pressure producing carbon monoxide andhydrogen.

Products of reaction are discharged from the reaction chamber 10 throughgas outlet 11 into a quench vessel 12 containing water and operated atsubstantially the generator pressure. The hot product gases leaving thegenerator through outlet 11 are conducted through pipe 13 to a pointbelow the surface 14 of water contained in the quench vessel. Water iscontinuously introduced through line 16 to a cooling ring 17 providedwith an annular outlet 18 adjacent the inner wall of pipe 13. Waterintroduced through the annular opening in the cooling ring helps coolthe gases and prevents overheating of pipe 13.

The lower end of pipe 13 is provided with serrations 19. A section ofpipe 13 between serrations 19 and liquid level 14 is provided withperforations 21. The combinatron of perforations and the serrationsserve to intimately contact the hot gases with water in the quenchvessel there- 'by providing almost instantaneous quench cooling of thegases.

Pipe 13 is supported from flange 23. A cylindrical shield 24 surroundsquench pipe 13 extending from a point below the bottom of pipe 13 to apoint near the upper end of vessel 12. Shield 24 is supported from pipe'18 by lugs 26. Spacer bars 27 extend from the lower part of the shieldto the wall of the vessel to maintain the quench pipe and shield inspaced relationship with the wall of the vessel.

Part of the quench water is introduced into the quench vessel throughline 16 as previously described. Additional quench water is supplied tothe vessel through line 28. Water is drawn from the quench vessel asrequired t9 maintain the desired liquid level through nozzle 30 and line31 controlled by valve 32 in response to liquid level controller 33.Vent 34 in pipe 13 above the liquid level of the water in the quenchvessel permits gases to enter pipe 13 when the flow of reactants isdiscontinued in reaction zone 10 so that water cannot be sucked from thequench vessel into the hot reaction chamber.

Quenched product gases pass through nozzle 35 into a product gas line 36controlled by valve 37. Nozzle 35 is disposed below the upper end ofshield 24 to prevent entrainment of water in the product gas streamwithdrawn through line 36.

In operation, steam and oil are introduced through line 4 and oxygenthrough line 8. The reactants are thoroughly mixed at the point ofdischarge into the reaction zone 10 by the burner 6. The reactants areproportioned, as controlled by valves 5 and 9, sothat partial combustiontakes place within the reaction chamber 10 at elevated temperature andpressure producing synthesis gas consisting essentially of carbonmonoxide and hydrogen which .is discharg d through outlet 11. Pipe 13conducts the hot synthesis gas from the reaction chamber into quenchvessel 12 where the gas is discharged into intimate contact with watercontained in the quench vessel through perforations 21, and, if needed,through serrations 19. The cooled gas, at approximately the temperaturecorresponding to the boiling point of the water at the pressure existingin the generator and quench vessel, is discharged through nozzle 35 andline 36, normally at uniform high pressure. Valve 37 is normally open.

To shut down the gas generator when it is desired to terminate the run,the flows of reactants to the generator are interrupted by closingvalves 5 and 9 and, at the same time, the withdrawalof reaction productsfrom the quench vessel is discontinued by closing valve 37. Since thewater in the quench vessel is normally at or near its boiling point atthe elevated pressure at which the generator is operated, it is evidentthat if the pressure in the system is lowered, for example by withdrawalof gases from line 37, water ;in the quench vessel flashes to steam. Asthe generator cools, this steam is drawn through outlet 11 into the hotgenerator. By closing the reactant inlets and the product gas outlet andbottling up the generator and quench vessel, this is prevented.Meanwhile, introduction ,of cooling water, optionally at a reduced flowrate, into the .quench vessel is continued. Excess water is withdrawnthrough line 31. As the temperature of the water within the quenchvessel drops, it is permissible to withdraw gases through line 36, ascontrolled by valve 37, to depressurc the system. The rate of pressurereduction must be controlled so that the pressure within the gasgenerator is maintained in excess of the vapor pressure of the water inthe quench vessel. To permit reduction of the pressure in the gasgeneration systern to atmospheric pressure, it is necessary that theWater in the quench vessel be cooled below about 212 F., the atmosphericboiling point of water.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. In a process wherein high temperature gases are produced byintroducing reactants into a reaction zone maintained at elevatedpressure and effecting reaction in said zone, and product gases arecontacted in a cooling zone maintained at substantially said elevatedpressure with a volatile cooling liquid having a boiling point below thetemperature at which said gases are produced, the method of shuttingdown the gas generation system which comprises discontinuing theintroduction of reactants to said reaction zone without substantialreduction in pressure therein, continuously supplying said coolingliquid to said cooling zone associated with said reaction zone at atemperature below the temperature corresponding to the boiling point ofsaid liquid at the existing pressure, and reducing the pressure in saidgas generation system by withdrawal of gas therefrom at a rate such thatthe pressure in said reaction zone is maintained in excess of the vaporpressure of the cooling liquid in said cooling zone.

2. ,A process as defined in claim 1 wherein said cooling liquid iswater.

3. A process as defined in claim 1 wherein said high temperature gasescomprise carbon monoxide.

4. In a process for the production of carbon monoxide and hydrogen byreaction of a carbonaceous fuel with an oxygen-containing gas atsuperatmosphen'c pressure in a compact reaction zone at an autogenouslymaintained temperature in the range of 1800 to 3500 F. wherein productsof reaction are contacted with water ina cooling zone maintained atsubstantially the pressure of said re action zone in an ,amountin excessof the amount required for saturation of the product gas at operatingpressure and at a temperature not above about 500 F., the improvement inshutting down the gas generation system which comprises discontinuingthe introduction of reactants to said reaction zone without substantialreduction in pressure therein, continuously supplying water to saidcooling zone associated with said reaction zone at a temperature belowthe temperature corresponding to the boiling point of the water at theexisting pressure, and reducing the pressure in said gas generationsystem by withdrawal of gas therefrom at a rate such that the pressurein said 10 reaction zone is maintained in excess of the vapor pressureof the water in said cooling zone.

5. A process as defined in claim 4 in which the temperature of the waterin said cooling zone is reduced to a temperature below 212 F. and thepressure in said reaction zone is subsequently reduced to atmosphericpressure.

6. A process as defined in claim 4 in which said carbonaceous fuel is aliquid hydrocarbon.

No references cited.

1. IN A PROCESS WHEREIN HIGH TEMPERATURE ARE PRODUCED BY INTRODUCINGREACTANTS INTO A REACTION ZONE MAINTAINED AT ELEVATED PLRESSURE ANDEFFECTING REACTION SAID ZONE, AND PRODFUCT GASES ARE CONTACTED IN ACOOLING ZONE MAINTAINED AT SUBSTANTIALLY SAID ELEVATED PRESSURE WITH AVOLATDILE COOLING LIQUID HAVING A BOILING POINT BELOW THE TEMPERATURE ATWHICH SAID GASES ARE PRODUCED, THE METHOD OF SHUTTING DOWN THE GASGENERATION SYSTEM WHICH COMPRISES DISCONTINUING THE INTRODUCTION OFREACTANTS TO SAID REACTION ZONE WITHOUT SUBSTANTIAL REDUCTION INPRESSURE THEREIN, CONTINUOUSLY SUPPLYING SAID COOLING LIQUID TO SAIDCOOLING ZONE ASSOCIATED WITH SAID REACTION ZONE AT A TEMPERATURE BELOWTH TEMPERATURE CORRESPONDING TO THE BOILING POINT OF SAID LIQUID AT THEEXSISTING PRESSURE, AND REDUCING THE PRESSURE IN SAID GAS GENERATDIONSYSTEM BY WITHDRAWAL OF GAS THEREFROM AT A RATE SUCH THAT THE PRESSUREIN SAID REACTION ZONE IS MAINTAINED IN EXCESS OF THE VAPOR PRESSURE OFTHE COOLING LIQUID IN SAID COOLING ZONE.